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At least 163 records · Page 9Linked to original sources
PubMed1995

5'-AMP inhibits dephosphorylation, as well as promoting phosphorylation, of the AMP-activated protein kinase. Studies using bacterially expressed human protein phosphatase-2C alpha and native bovine protein phosphatase-2AC.

Human protein phosphatase-2C alpha (PP2C alpha) was purified to homogeneity after expression in Escherichia coli. AMP inhibited the dephosphorylation of AMP-activated protein kinase (AMPK), but not phosphocasein, by PP2C alpha. The concentration dependence and the effects of other nucleotides (ATP and formycin A-5'-monophosphate) suggest that AMP acts by binding to the same site which causes direct allosteric activation of AMPK. A similar, although less pronounced, effect was observed with another protein phosphatase (PP2AC). We have now shown that AMPK activates the AMPK cascade by four mechanisms, which should make the system exquisitely sensitive to changes in AMP concentration.

AMP-Activated Protein Kinases↗
PubMed1983

Forskolin-induced cyclic AMP production and gastric acid secretion in dispersed rabbit parietal cells: novel evidence for a major role of cyclic AMP in acid release.

Forskolin, a unique diterpine which is a direct activator of cyclic AMP-generating systems, stimulated both cyclic AMP and acid production in dispersed rabbit parietal cells. This agent was also capable of augmenting the action of histamine on both cyclic AMP and acid production at a low concentration. These findings provided novel evidence for a major role of cyclic AMP in gastric acid secretion.

Animals↗
PubMed1986

The use of cyclic AMP efflux studies in attempts to determine the effects of morphine on cyclic AMP formation in striatal slices.

The effect of morphine and naloxone on basal and forskolin-stimulated efflux of cyclic AMP from rat striatal slices was examined. Neither morphine nor naloxone had any consistent effect on the basal efflux of cyclic AMP. Forskolin produced a time and dose-dependent enhancement of cyclic AMP efflux. Neither morphine nor naloxone affected this forskolin-enhanced release. These results suggest that measurements of cyclic AMP released from brain slices do not accurately reflect effects on adenylate cyclase inhibition by opiates.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1986

Activation of trout gill AMP deaminase by an endogenous proteinase--III. Comparative studies on the gill AMP deaminase from different fresh water and sea water teleosts.

The effects of monovalent cations and inorganic phosphate, on gill AMP deaminase, were compared in different fresh water and sea water stenohaline and euryhaline Teleosts. Generally, sea water species displayed a lower sensitivity to these effectors than fresh water species. During salinity changes, the sensitivity of gill AMP deaminase to cations and phosphate were modified proportionally to the tolerance of a given species to variations of environmental salinity. In particular, these parameters were modified in the weak euryhaline, Salmo gairdneri, but not in the real euryhaline, Anguilla anguilla. In sea water adapted trout, the appearance of a modified AMP deaminase form, with similar properties to that found in sea water species, is suggested. When compared with the conclusions from the preceeding papers [Raffin (1986) Comp. Biochem. Physiol. 85B, 157-162; 85B, 163-171], the results suggest that modification of gill AMP deaminase by limited proteolysis should be a rather general adaptation mechanism to stress.

AMP Deaminase↗
PubMed1989

Comparison of kinetic and regulatory properties of high S0.5 form of AMP deaminase from chicken and pigeon liver with AMP deaminase from rat and ox liver.

1. The high S0.5 form of AMP deaminase from avian liver was shown to display a two times lower S0.5 value than the single mammalian enzyme form. 2. Avian enzymes showed several fold higher affinity to the activator (ATP) but lower affinity to inhibitors (GTP and Pi) than the mammalian AMP deaminases. 3. GTP was shown to exert a biphasic: activating and inhibitory effect on all the enzymes tested, the chicken and pigeon enzymes being activated within a much broader range of effector concentration. 4. In the presence of 3 mM ATP the activity of avian enzymes was not affected by high GTP and Pi concentrations, in contrast to AMP diaminase from rat liver which was strongly inhibited by GTP under the same experimental conditions. 5. The differences of the regulatory properties described are discussed in terms of adjustment of avian liver AMP deaminase to a faster adenylates' catabolism and thus urate synthesis.

AMP Deaminase↗
PubMed2000

The design of cyclic AMP--recognizing oligopeptides and evaluation of its capability for cyclic AMP recognition using an electrochemical system.

A novel 17-mer peptide ligand for cyclic AMP was designed using the amino acid sequences of essential subsites in various cyclic AMP-dependent protein kinase (protein kinase A) families. The Au disk electrode, which was modified with the designed 17-mer oligopeptide, responded to cyclic AMP but virtually did not respond to any other cyclic nucleotides using the ion channel sensor mechanism. On the other hand, a scrambled peptide, which had the same amino acid composition as and had an amino acid sequence different from the 17-mer oligopeptide, did not respond to any nucleotides. This indicates that the designed 17-mer peptide actually acted as a selective ligand for cyclic AMP. This ligand-designing strategy using peptide sequences in target-binding proteins may possibly be extended to the design of peptide ligands for other second messengers.

Cyclic AMP↗
PubMed1974

Cyclic AMP-mediated induction of the cyclic AMP phosphodiesterase of C-6 glioma cells.

Long-term regulation of the cyclic nucleotide phosphodiesterase of the C-6 rat glioma cell line has been studied. Both the low K(m) and high K(m) activities can be induced by elevation of intracellular cyclic AMP levels following either dibutyryl cyclic AMP or norepinephrine treatment of the cells. The enzymes are maximally induced by 3-4 hr. The presence of either cycloheximide or actinomycin D prevents induction by either dibutyryl cyclic AMP or norepinephrine. Evidence is presented that the norepinephrine effect is mediated by the beta-catecholamine receptor. The increased phosphodiesterase activity causes a partial refractoriness to a second challenge with norepinephrine, which can be overcome by blockade of the induction with cycloheximide. The results suggest that just as short-term regulation of cyclic AMP levels occurs via changes in the rates of synthesis or degradation, long-term alterations of the system may also involve either the adenylate cyclase or the phosphodiesterase.

Animals↗
PubMed1978

Cyclic AMP accumulation in psoriatic skin: differential responses to histamine, AMP, and einephrine by the uninvolved and involved epidermis.

Using the uninvolved and involved skin from psoriatic patients, we investigated the effects of histamine and AMP (or adenosine) in vitro on the intracellular cyclic AMP levels. Both agents activated adenylate cyclase of the uninvolved and involved resulting in the accumulation of cyclic AMP. Without a cyclic nucleotide phosphodiesterase (PDE) inhibitor, these responses were biphasic and the maximal accumulation was observed in 5 min. With the PDE inhibitor both responses were markedly potentiated and high levels of cyclic AMP were observed for more than 20 min. The response to histamine by the involved skin was much greater than that by the uninvolved. The degree of the response to adenosine was approximately equal. In accordance with our previous work, the response to epinephrine by the involved skin was much less than that by the uninvolved. Thus adenylate cyclases of involved skin from psoriatic patients exhibit a markedly diminished response to epinephrine while at the same time exhibiting a markedly enhanced response to histamine. This precludes the possibility that the unresponsiveness to epinephrine can be due to a generalized inability of the epidermal psoriatic plaque cell to make a functioning cell membrane.

Adenosine Monophosphate↗
PubMed1985

Inhibitory effect of methacholine on drug-induced relaxation, cyclic AMP accumulation, and cyclic AMP-dependent protein kinase activation in canine tracheal smooth muscle.

Functional antagonism between bronchoconstricting and bronchodilating pathways was examined in canine tracheal smooth muscle. Trachealis strips were contracted with either 0.3 microM (EC55) or 3.0 microM (EC80) methacholine before being relaxed by the cumulative addition of isoproterenol, prostaglandin E2, or forskolin. The EC50 for all three relaxants was increased 10-fold in tissues contracted with 3.0 microM methacholine vs. those contracted with 0.3 microM methacholine. Moreover, contracting tissues with the higher concentration of methacholine reduced the maximum relaxation induced by prostaglandin E2 and isoproterenol. Forskolin produced total relaxation regardless of the concentration of methacholine used and thus was a much more effective bronchodilator than either isoproterenol or prostaglandin E2. The inhibitory effect of methacholine on the relaxant response to these agents was paralleled by a reduction in drug-stimulated cyclic AMP-dependent protein kinase activity. Methacholine reduced the maximum activation of cyclic AMP-dependent protein kinase elicited by isoproterenol, prostaglandin E2 and submaximal concentrations of forskolin, which was a much more powerful enzyme activator than the other two agents. The ability of a maximum concentration of forskolin (30 microM) to activate cyclic AMP-dependent protein kinase was not inhibited by methacholine. Although methacholine also appeared to suppress drug-stimulated cyclic AMP accumulation, the inhibitory effect was only statistically significant in forskolin-treated tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1973

Studies on cellular autophagocytosis. Cyclic AMP- and dibutyryl cyclic AMP-stimulated autophagy in rat liver.

Intraperitoneal injections of either cyclic AMP or dibutyryl cyclic AMP are capable of producing a wave of autophagy in rat liver which resembles closely that stimulated by glucagon. These autophagic vacuoles are acid-phosphatase-positive and appear to arise via the envelopment of organelles by double-walled cisterna. At later times these autophagic vacuoles are usually surrounded by a single membrane. Injection of equimolar amounts of 5'-AMP failed to produce a wave of autophagy. These findings constitute preliminary evidence that glucagon-stimulated autophagy is mediated at least in part by cyclic AMP.

Animals↗
PubMed1985

Selective increase of R-I subunit of cyclic AMP-dependent protein kinase in glia-rich primary cultures upon treatment with dibutyryl cyclic AMP.

Levels of cyclic GMP-dependent protein kinase and of the subunits (R-I, R-II and C) of cyclic AMP-dependent protein kinase were determined in two types of neural primary cell cultures that were either treated or not treated with dibutyryl cyclic AMP. Astroglia-rich cell cultures from newborn rat brain responded to exposure to dibutyryl cyclic AMP by a 2-3-fold increase in the level of R-I subunit, as demonstrated by two radioimmunological procedures, while the levels of the other subunits (R-II and C) and of cyclic GMP-dependent protein kinase remained unaffected. In contrast, neuron-rich cell cultures from embryonic rat brain did not display such a change in the level of R-I subunit. Thus, the elevation in the level of R-I elicited by dibutyryl cyclic AMP in normal non-malignant neural cells in culture was restricted to glial rather than neuronal cells.

Animals↗
PubMed1988

The low activity of acetyl-CoA carboxylase in basal and glucagon-stimulated hepatocytes is due to phosphorylation by the AMP-activated protein kinase and not cyclic AMP-dependent protein kinase.

Acetyl-CoA carboxylase purified from isolated hepatocytes is activated dramatically by protein phosphatase treatment, concomitant with a reduction of the phosphate content from 3.7 to 1.1 mol/subunit. Glucagon treatment of the cells produces a further inactivation of the enzyme that is totally reversed by phosphatase treatment, and is associated with an increase in phosphate content of 0.8 mol/subunit, distributed in two peptides which contain the sites phosphorylated in vitro by the cyclic AMP-dependent and AMP-activated protein kinases. Sequencing of these peptides shows that the low activity of acetyl-CoA carboxylase is due to phosphorylation by the AMP-activated protein kinase, and not cyclic AMP-dependent protein kinase, even after glucagon treatment.

Acetyl-CoA Carboxylase↗
PubMed1997

Major changes in the kinetic mechanism of AMP inhibition and AMP cooperativity attend the mutation of Arg49 in fructose-1,6-bisphosphatase.

The significance of subunit interface residues Arg49 and Lys50 in the function of porcine liver fructose-1,6-bisphosphatase was explored by site-directed mutagenesis, initial rate kinetics, and circular dichroism spectroscopy. The Lys50 --> Met mutant had kinetic properties similar to the wild-type enzyme but was more thermostable. Mutants Arg49 --> Leu, Arg49 --> Asp, Arg49 --> Cys were less thermostable than the wild-type enzyme yet exhibited wild-type values for kcat and Km. The Ki for the competitive inhibitor fructose 2,6-bisphosphate increased 3- and 5-fold in Arg49 --> Leu and Arg49 --> Asp, respectively. The Ka for Mg2+ increased 4-8-fold for the Arg49 mutants, with no alteration in the cooperativity of Mg2+ binding. Position 49 mutants had 4-10-fold lower AMP affinity. Most significantly, the mechanism of AMP inhibition with respect to fructose 1,6-bisphosphate changed from noncompetitive (wild-type enzyme) to competitive (Arg49 --> Leu and Arg49 --> Asp mutants) and to uncompetitive (Arg49 --> Cys mutant). In addition, AMP cooperativity was absent in the Arg49 mutants. The R and T-state circular dichroism spectra of the position 49 mutants were identical and superimposable on only the R-state spectrum of the wild-type enzyme. Changes from noncompetitive to competitive inhibition by AMP can be accommodated within the framework of a steady-state Random Bi Bi mechanism. The appearance of uncompetitive inhibition, however, suggests that a more complex mechanism may be necessary to account for the kinetic properties of the enzyme.

Adenosine Monophosphate↗
PubMed1995

High efficiency of glycerol 2-phosphate and sn-glycerol 3-phosphate as nucleotidyl acceptors in snake venom phosphodiesterase esterifications. Formation of primary and secondary AMP-O-glyceryl and AMP-O-glycerophosphoryl esters and evidence for an acceptor-binding enzyme site.

Snake venom phosphodiesterase (SVP) catalyzes the alcoholysis of ATP by primary R-CH2OH alcohols with uncharged R residues, yielding AMP-O-CH2R esterification products. The alcohols compete with water for an SVP-bound adenylyl intermediate. In this study, it has been shown that SVP also catalyzes the reactions of glycerol 2-phosphate and sn-glycerol 3-phosphate with ATP to yield AMP-O-glycerophosphoryl esters. The products were identified by HPLC, the dependency of the reactions on glycerol phosphates, ultraviolet spectroscopy, and conversion to AMP by phosphodiesterase, or to AMP-O-glyceryl esters by alkaline phosphatase. The results demonstrated that R-CH2OH alcohols with negatively charged R residues, as well as secondary alcohols, act as adenylyl acceptors in SVP reactions, thus extending the usefulness of SVP as a tool to produce 5'-nucleotide derivatives. The efficiencies (EA) of glycerol phosphates as adenylyl acceptors were very high at low, millimolar concentrations, but decreased abruptly when the acceptor concentration was increased and, for glycerol 2-phosphate, when Pi or NaCl was present. In contrast, glycerol EA was independent of its own concentration, Pi, and NaCl. The responses of glycerol phosphates indicate that they act as adenylyl acceptors via a mechanism different from uncharged R-CH2OH alcohols. The occurrence of an acceptor-binding enzyme site, specific for negatively charged R residues, and its potential relevance to the in vivo role of 5'-nucleotide phosphodiesterases as 5'-nucleotidyl transferases are discussed.

Adenosine Monophosphate↗
PubMed1991

Regulation of fungal proteolysis on cyclic AMP-dependent protein kinase, cyclic AMP phosphodiesterase, glycogen synthase and histones.

Limited proteolysis of catalytic and regulatory subunits of cyclic AMP-dependent protein kinase (A-pk), cyclic AMP phosphodiesterase, glycogen synthase, and histones by fungal protease (type XIX) was analyzed by the digested peptide bands in SDS polyacrylamide gel electrophoresis. The modulatory effects on proteolysis by nucleotides, polypeptides, and phospholipids may greatly depend on the intrinsic nature of substrates. The proteolysis of the regulatory subunit of A-pk and glycogen synthase was not regulated by nucleotides and nucleic acids. In comparison, phosphatidyl serine, cardiolipin, and pepstatin A stimulated the proteolysis of the catalytic subunit of A-pk. Whereas, lambda DNA (Hind III digest), t-RNA, GTP-, phosphatidyl serine, sphingosine inhibited the proteolysis of cyclic AMP phosphodiesterase. Moreover, MS2 RNA, lambda DNA, t-RNA, dGTP, Phosphatidyl serine, phosphatidyl inositol, antipain, and chymostatin exerted inhibitory proteolytic effect on histone VIII-S. Some of these agents also had similar inhibitory effect on other types of histones (types III-S and VII-S). The inhibitory effect of phosphatidyl serine on proteolysis of histone may be due to their interaction which was monitored by the drastic increase of uv absorbance.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1998

Fencamfamine modulates sodium, potassium-ATPase through cyclic AMP and cyclic AMP-dependent protein kinase in rat striatum.

Dopamine (DA) and fencamfamine (FCF) modulatory action on Na,K-ATPase and Mg-ATPase activity were evaluated in rat striatum. DA and FCF induced a decrease in Na,K-ATPase, without affecting Mg-ATPase activity. The effect of FCF was dose-dependent from 10 to 100 microM, with an IC50 of 4.7 x 10(-5) M. Furthermore, the effect of FCF (100 microM) increasing AMPc levels, but not GMPc, was nonadditive with that of DA (10 microM), which is consistent to a common site of action. The 8-bromo-cyclic AMP also induced a specific reduction in the Na,K-ATPase activity. The reduction of Na,K-ATPase induced by FCF (100 microM) was blocked by either SCH 23390 or sulpiride, which are D1 and D2 receptor antagonists. The decrease in striatal NA,K-ATPase activity induced by FCF was blocked by KT 5720, a selective inhibitor of cyclic AMP-dependent protein kinase (PKA), but not by KT 5823, a selective inhibitor of cyclic GMP-dependent protein kinase (PKG). Otherwise, KT 5720 or KT 5823 did not produce any change in Na,K-ATPase or Mg-ATPase activity. These data suggest that FCF reduces Na,K-ATPase activity through cyclic AMP-dependent changes in protein phosphorylation via a PKA mechanism.

Animals↗
PubMedDate not supplied

The synthesis and characterisation of a cyclic AMP-Sepharose 4B matrix with affinity for cyclic AMP-dependent proteins.

A novel synthesis route for the preparation of a cyclic AMP-containing affinity adsorbent is described. This involves the use of a simple single-vessel, two-step, solid-phase reaction in which 5'-AMP, originally coupled to the matrix in the form of 5'-AMP-Sepharose 4B, is cyclised by a sequence involving activation of the phosphate moiety, followed by intramolecular condensation to give a 3',5'-phosphodiester. Physicochemical evidence, including 31P NMR studies, shows that this cyclisation takes place leaving no trace of original phosphomonoesters. The gel retains its excellent chromatographic properties, but now its specificity is directed towards cAMP-dependent proteins. Protein kinase (EC 2.7.1.37) binds to the gel, the catalytic subunit only being eluted when a simple buffer 0.2 M phosphate/1 mM theophylline is applied to column, whilst the regulatory unit is eluted using 20% ethylene glycol of 2% Pharmalyte, pH 5-8. This gel should find a use in the purification of protein kinase subunits and, by inference, of other cAMP-dependent proteins.

Adrenal Cortex↗
PubMed1993

Role of ischemia-reperfusion on myocardial cyclic AMP and cyclic AMP phosphodiesterase: effects of amrinone on regional myocardial force and shortening.

This study tested the hypothesis that a reperfused ischemic myocardial region of the dog heart would be unable to increase its function in response to amrinone, a specific cyclic AMP phosphodiesterase (cAMP-PDE) inhibitor, due to loss of cAMP-PDE activity in the region. The global contractility (+dp/dtmax), regional percent shortening (ultrasonic crystals), and developed force (miniature force gauge) were measured on a continuous basis throughout a 6-hour experiment and regional blood flow (radioactive microspheres) in open-chest pentobarbital-anesthetized mongrel dogs. The left anterior descending coronary artery (LAD) was isolated and ligated for 2 hours and allowed to reperfuse for 4 hours. This myocardial region was compared to a nonischemic region supplied by the circumflex artery. At the end of the 4-hour reperfusion period, 9 dogs were treated with amrinone (5 mg/kg) and three dogs were not treated with amrinone. The hearts were rapidly excised and frozen in liquid nitrogen. Cyclic AMP and cAMP-PDE activity was determined in homogenates of myocardial tissue. Blood flow decreased during occlusion in the LAD region and returned toward control with reperfusion. Flow increased nonsignificantly with amrinone. the basal cyclic AMP content of the two regions was not different. The cAMP-PDE activity was reduced 24% in the LAD region compared to the control region. There were no ischemia-induced changes in the enzyme characteristics. These experiments demonstrated increased global function in the ischemic reperfused myocardium after amrinone was administered (dP/dtmax: 2092 +/- 538 to 3277 +/- 688 mmHg/sec).(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗